Federal antitrust regulators have granted agribusiness giants Bayer and Monsanto permission to merge after the two companies agreed to spin off $9 billion worth of assets, the largest such sale of corporate assets ever required by the Justice Department.

Under the proposed settlement filed Tuesday, Bayer will sell its seed and herbicide businesses to a third party, the German chemical company BASF. It also will sell its emerging digital farming business as well as a variety of intellectual property and R&D projects.

The targeted spinoffs are aimed at preventing Bayer and Monsanto from using their combined control over seeds and seed treatments to raise the price of agricultural products to farmers and consumers, Justice Department officials said. Just six companies, including Bayer and Monsanto, have historically dominated the global trade in seeds and agrochemicals.

The $66 billion deal already has received approval from regulators in the European Union, Russia and Brazil, making the U.S. approval one of the last major hurdles. Bayer said it expects to complete the merger by midsummer.

“Receipt of the DOJ’s approval brings us close to our goal of creating a leading company in agriculture,” Bayer chief executive Werner Baumann said in a statement.

U.S. antitrust officials investigated the Bayer-Monsanto deal for more than a year, ultimately concluding that it could result in increased costs for the country’s agricultural sector.

Both companies produce genetically modified cotton, canola and soybean seeds, as well as the pesticides that pair with them. Under the original deal, Bayer would have acquired a monopoly over herbicide-resistant cotton and canola in the United States and a near monopoly in some other crops, including cucumbers and carrots, the Justice Department found.

“America’s farm system is of critical importance to our economy, our food system and our way of life,” Makan Delrahim, the Justice Department’s top antitrust enforcer, told reporters Tuesday. “America’s farmers rely on head-to-head competition between Bayer and Monsanto.”

In addition to eliminating a direct competitor in some lines of business, the deal as proposed would have led to Bayer gaining anticompetitive leverage in other markets, according to the Justice Department.

By merging with Monsanto, regulators found, Bayer would become a major supplier of corn seed. After the merger, Bayer, which also sells a key seed treatment to corn farmers, would have an incentive to raise the price of the treatment knowing that farmers would have fewer choices of seed suppliers, the government alleged.

Regulators also ruled that Bayer and Monsanto would lose motivation to develop new crops, treatments and pesticides as a result of the merger. To address those concerns, the Justice Department will require Bayer to transfer several research facilities and projects to BASF, including a research center in North Carolina and a bank of soybean tissue samples used to develop new products.

“The proposed remedies will ensure that BASF can step into Bayer’s shoes, thereby preserving the competition that the merger would otherwise destroy,” the government said.

Concerns about competition have grown thanks to a wave of megamergers in the agricultural industry. Regulators last year signed off on mergers between DuPont and Dow Chemical, as well as ChemChina and Syngenta, concentrating global agrochemical research and sales in the hands of five companies.

The Monsanto-Bayer merger will further shrink that number to four, raising questions about the future of agricultural competition and innovation. Some critics of the deal said they were not satisfied by the terms disclosed Tuesday.

“Today’s news makes it clear that our antimonopoly laws are completely worthless and the U.S. Department of Justice merger review process is pointless,” said the Organization for Competitive Markets, a farm group that opposes megamergers, in a statement.

Angela Huffman, a spokeswoman for the group, added that while it could not yet predict the full impact on farmers, OCM expects the deal to raise seed and pesticide costs. That probably will have little impact on consumers, given that farm expenses account for only a small portion of food prices.

Bayer has defended the deal as the surest way to increase agricultural productivity as the world’s population grows, citing Monsanto’s advantage in plant genetics and Bayer’s portfolio of pesticides and other chemicals.

“Farmers will benefit from a range of new, superior solutions aimed at helping to advance the next generation of farming and to address some of society’s most pressing challenges,” the company says on a website advocating for the settlement.

The landmark settlement, if approved by a judge, would be a major victory for Delrahim, who was confirmed as President Trump’s assistant attorney general for antitrust issues last summer. Delrahim has argued that selling off assets is a more effective way to resolve anticompetitive mergers than forcing companies to abide by requirements that must be reviewed by regulators on an ongoing basis.

Tuesday’s settlement required close cooperation from the top executives of Bayer and Monsanto, said Justice Department officials, speaking on the condition of anonymity to discuss closed-door negotiations.

The chief executives of both companies traveled to Washington over the Easter holiday to be briefed about the government’s concerns with the deal, the government said.

Brian FungBrian Fung covers business and technology for The Washington Post. Before joining The Post, he was the technology correspondent for National Journal and an associate editor at the Atlantic. Follow

Caitlin DeweyCaitlin Dewey is The Washington Post's food policy writer for Wonkblog. She previously covered digital culture and technology for The Post.